Study Of Biodegradable Iron Alloys Based On Electrodeposition

Iron?Fe?based materials have some advantages,such as good biocompatibility,excellent mechanical properties,outstanding machinability and low cost,and so on.Therefore,iron based materials are one of the most studied biodegradable metal materials.However,the degradation rates of the iron based materials are low.In the current studies,it is one of the major purposes to increase the degradation rates of the iron based materials.It is not only likely to increase the degradation rates,but also to improve the mechanical properties and biocompatibility that adding alloying elements into iron matrix.Hence,alloying is a promising method.Electrodeposition has many advantages,such as sound theoretical basis,simple devices and simple operation,and so on.More importantly,metal layers can be prepared on the complex shaped substrates by electrodeposition.It provides a feasibility to prepare the complex shaped devices.Furthermore,except for pure metals,alloys can also be prepared by the method.The characteristics of the materials,such as microstructures,components and mechanical properties,and so on,can be changed through adjusting the process parameters.Therefore,electrodeposition is one of the good methods for preparing the biodegradable metal materials.In this work,a study on the preparation of biodegradable iron alloys using electrodeposition was performed.Fe-Pd,Fe-Zn and Fe-W alloy were prepared.Based on the preparation of the Fe-W alloy,a novel porous Fe/Fe-W alloy scaffold with a double-layer structured skeleton was also prepared.Their microstructures,tensile strength,degradability and biocompatibility were studied by scanning electron microscopy?SEM?,energy-dispersive X-ray spectroscopy?EDS?,X-ray diffractometer?XRD?,X-ray photoelectron spectroscopy?XPS?,mercury porosimetry,tensile test,immersion,electrochemistry,in vitro and in vivo method.The microstructures and components of the Fe-Pd alloys were mainly affected by Pd concentrations in the electrolytes.The alloys with high Pd content and coarse surface were obtained under high Pd concentrations in the electrolytes.After heat treatment,phase transition of the alloys was occurred from body-centered cubic phase to FePd intermetallic compound which is face-centered cubic phase and Fe_0.97Pd_0.03.03 which is body-centered cubic phase.After immersion tests,an obvious corrosion of Fe-Pd alloys was occurred.The corrosion products were mainly composed of Ca-P compounds,PdO and Fe₂O₃.The corrosion rates of the Fe-Pd alloys were obviously higher than that of pure Fe.The spreading shapes of the cells adhered on the surface were good.The effects of Zn ion concentrations in the electrolytes on the Zn contents in the Fe-Zn alloys were not distinct.However,the phase compositions and morphologies of the alloys could be significantly affected by the concentrations.With the increase of Zn ion concentrations,the phase changed from heterogeneous to single phase and a flat surface was created.Moreover,the components,microstructures and phase compositions could also be affected by the current densities to some extent.In immersion tests,the corrosion rates of the alloys were different obviously,and it could be affected by Zn contents and the corrosion products on the surface.With the increase of the Zn contents in the alloys,the corrosion rates increased first then decreased.The corrosion products were mainly ZnO and Ca-P compounds.In electrochemistry tests,a similar corrosion rate was obtained as the Zn contents were low.The corrosion rates were increased obviously as the Zn contents were high.The corrosion rates of the Fe-Zn alloys were higher than that of pure Fe.The cells adhered on the surface showed different spreading shapes.The composition of the Fe-W alloys could not be affected by the concentrations of main salt ions.Phase transition was not generated by heat treatment.The electrochemical corrosion rates of Fe-W alloys were faster than that of pure Fe.In the preparation of the pure Fe scaffold,the polyurethane template in the skeleton of the scaffold could be cleaned and the flaws on the skeleton could also be eliminated by heat treatment.The scaffolds with different-sized pores could be easily prepared by selecting template with different-sized pores.Based on the above research works,a novel porous scaffold with a double-layer structured skeleton was prepared by a two-step electrodeposition.The microstructures,tensile strengths and apparent densities of the scaffolds were similar to that of cancellous bone.The tensile strengths and the apparent densities could be enhanced by increasing electrodeposition time of pure Fe scaffolds served as substrates.The skeleton of the scaffolds was composed of a hollow Fe skeleton wrapped in a thin layer of Fe-W alloy.The corrosion rates decreased gradually as the immersion time increased.The major corrosion products were composed of Fe₂?WO₄?₃ and Fe₂O₃.The cell viability was closely related to the corrosion rates.A low corrosion rate would lead to high cell viability.In general,the scaffolds have good in vitro biocompatibility.Fe-Pd,Fe-Zn and Fe-W alloy showed the different corrosion properties,which provides a possibility for preparing biodegradable metals with controllable corrosion rates.The in vivo tests of Fe-Zn alloy showed that an obvious degradation was generated,and the degradation products include Zn compounds and Ca-P compounds.After implantation for 28 days,the inflammatory responses in the tissue in the vicinity of the implant disappeared basically.In general,Fe-Zn alloy showed excellent biocompatibility.